Closes #396: Document circumventing of UAC for Free Space Erasures.
A short paragraph has been added, indicating the background and the most common workaround for the problem. A link to the forum where all documented workarounds are also provided.

Merged revision(s) 2326 from trunk/eraser: The title of the balloon tip should be "Task Completed" and not "Task Executed" for clarity. This was suggested by Jackjack in #388.
Fixes #388: balloon tips wording post wiping

We can use a higher significance level of 0.5; this yields slightly more accurate ETAs since more false samples are rejected (some good ones are rejected too -- but that's okay as we intend to just make this a little more elaborate than simple averages)

The event handler for the checked changed event for each of the recurring schedule types may be called from outside the three buttons. For such instances, do not change the checked state (since sender is none of the three, all will be reset to blank)

Be explicit about the behaviour of the schedule check boxes. Since we handle the checking ourselves, we need to be careful of when the boxes are triggered and reset the states properly. Fixes the bug described in ​http://bbs.heidi.ie/viewtopic.php?p=24697#p24697